With the development of semiconductor technologies, the integration degree of ultra-large-scale integrated circuits has been developed to include as many as hundreds of millions or even billions of device units, and a multi-layer (more than two layers) metal interconnection technology has been widely used. Conventionally, the metal interconnect is made of aluminum metal. However, as the feature size of the device in an integrated circuit chip continues to decrease and the circuit density in a metal interconnect continues to increase, the response time needs to be reduced and the conventional aluminum interconnects are no longer meet requirements. As such, the copper interconnects have gradually replaced the aluminum interconnects. Compared with the aluminum metal, the copper metal has a lower electrical resistivity and a higher resistance to electromigration, to reduce the resistance capacitance (RC) delay of the interconnects and improve the electromigration and enhance device stability.
However, the copper interconnects also have drawbacks. The copper metal has a high mobility, and copper can diffuse very fast in silicon and silicon oxides and most dielectrics. Once copper is introduced into the semiconductor substrate or the dielectric layer, the lifetime of the minority carriers in a device will be affected, causing a leakage current and an increase in the electromigration of the interconnection structure. As a result, circuit failure may occur, and the reliability is reduced. One solution is to form a barrier layer on the substrate before forming the copper interconnect, which can refrain the diffusion of copper to a certain extent.
However, the barrier performance of the barrier layer against copper diffusion in a copper interconnect is relatively week, and copper can easily diffuse into the dielectric layer, deteriorating the performance of the dielectric layer. The disclosed semiconductor structure and fabrication method are directed to solve one or more problems set forth above and other problems in the art.